The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the inventor hereof, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted to be prior art against the present disclosure.
Certain kinds of electronic circuits suffer from performance degradation at higher temperatures. For example, at least some operational amplifiers suffer from decreased bandwidth at higher temperatures. One solution to mitigate such performance degradation at higher temperatures is to provide the circuit in question (e.g., an operational amplifier) with a bias current generator that produces a temperature-dependent bias current that is proportional to temperature—in other words, whose output bias current increases generally linearly as temperature increases. For example, one way to compensate for performance degradation at higher temperatures is to use a bias current generator based on a constant-transconductance current (or constant Gm current, ICGM), or on a proportional-to-absolute-temperature current (or PTAT current, IPTAT). However, such a bias current generator typically generates a smaller bias current at lower temperatures which could cause performance degradation at the lower temperatures.
An alternative solution is to provide a bias current generator that outputs a temperature-independent constant current (ICX) or a poly-resistor-dependent constant current (IPP) (that is, a current that is kept constant as temperature changes based on the changing resistance of a temperature-dependent polysilicon resistor). However, if a constant current is made large enough to provide acceptable performance at higher temperatures, then at lower temperatures—possibly even at room temperature—the bias current would be higher than necessary, wasting power.